1. Field of the Invention
This invention relates to a high-resolving-power solid-state image pickup device comprising a solid-state image sensor and a mosaic microfilter. A mosaic microfilter is an array of minute filter elements one element per photoelectric sensor element of the pickup device.
2. Description of the Prior Art
A method of forming a solid-state image pickup device for color image is well known in the art. This method arranges a mosaic or a line type microfilter on a solid image sensor. The solid-state image sensor comprises a light receiving section, a charge transferring section and a transfer control section. The terms "solid-state image sensor" and "solid-state image pickup device" basically mean the same thing. However, for convenience in description, the term "a solid-state image sensor" as used herein is intended to mean one for monochromatic light which is used to detect only an image brightness, and the term "solid-state image pickup device" as used herein intended to mean the assembly of the solid-stage image sensor and the microfilter. The light receiving section comprises a plurality of photoelectric conversion elements arranged in a matrix form, and microfilters are so arranged that the elements of its mosaic correspond to each of the photoelectric conversion elements, that is, one color is assigned to one photoelectric conversion element. For instance, of three colors R(red), G(green) and B(blue), R is assigned to one photoelectric conversion element.
There are a variety of systems to arrange the red, green and blue filters in a mosaic pattern, and the colors of the filters may be complementary colors cyan(Cy), magenta(Mg) and yellow(Ye), and white(W).
Fundamentally, if the red, green and blue filters are repetitively arranged, in the stated order, according to the scanning sequence, then the color signals are obtained at a uniform frequency. However, in the system, the same color signals are obtained in a three-picture-element synchronization mode, and therefore the horizontal resolution is lowered to one-third (1/3). In practice, in order to prevent the apparent lowering of the resolution, a so-called "Bayer's arrangement" is effectively employed for arrangement of the filters. In the arrangement, the filters on lines corresponding to the odd-numbered scanning lines are arranged in the order of R,G,R,G, . . . , while filters on lines corresponding to the even-numbered scanning lines are arranged in the order of G,B,G,B, . . . In this case, the image signal of the previous scanning line is delayed by a 1H (one horizontal scan period) delay line and combined with the image signal of the present scanning line; that is, combination of the image signals of two adjacent scanning lines forms any color signal within a period of at least two picture elements.
In another conventional solid-state image pickup device for color images, the mosaic microfilters have the colors R(red), G(green), R, G, . . . on the first and second lines, and the colors G(green), B(blue), G, B, . . . on the third and fourth lines. The arrangement of these four lines is repeated. In order to form a television image field signal according to an interface system, first the odd-numbered lines of the solid-state image pickup device are successively read, and a 1H delay line is used so that R, and G and B signals are formed by utilizing the image signals read out of two lines. In this operation, a luminance signal Y is formed through weighted addition according to the following equation: EQU Y=0.11B+0.59G+0.3R
According to this, color difference signals R-Y and B-Y can also be formed.
In the case where an interlaced scanning operation with alternating A and B fields is carried out when the "Bayer's arrangement" is employed, the (2n+1)th and the (2n+2)th line are combined for the A field (where n may be zero and or a positive integer) while the (2n+2)th and the (2n+3)th line are combined for the B field, so that images signals corersponding to the respective scanning lines are formed. This interlaced scanning operation is, in a sense, carried out for convenience, and therefore the resolving power in the vertical direction is lowered.